In conventional mobile communication systems, especially mobile communication systems based on a 3GPP standard, there have been two ways of bandwidth allocation to a data path (here, which is particularly called a bearer in conformity to the 3GPP standard) when a mobile terminal performs packet communication with a correspondent node through a core network. One is to apply GBR (Guaranteed Bit Rate), and a bearer based thereon is called a GBR bearer. The other is not to apply GBR, and a bearer based thereon is called a non-GBR bearer.
The GBR bearer is a bearer to which guaranteed QoS is applied, and guaranteed values related to transmission delay, packet loss, transmission rate, and the like, such as QCI (QoS Class Identifier), GBR (Guaranteed Bit Rate), and MBR (Maximum Bit Rate), as disclosed in Non-Patent Document 2 cited below are set. The QCI is an identifier (ID) for identifying multiple QoS profiles defined for transmission precedence, transmission delay budget, packet loss budget, or the like. A gateway (called PDN-GW or PGW (Packet Data Network Gateway) in Non-Patent Document 2) for forwarding packets transmitted from or received by a mobile terminal (UE) may discard packets in UE traffic exceeding GBR or MBR.
The non-GBR bearer is a bearer to which parts of QoS is guaranteed, and guaranteed values related to transmission delay, packet loss, APN/UE-based transmission rate, and the like, such as QCI, APN-AMBR (Per APN Aggregate Maximum Bit Rate), and UE-AMBR (per UE Aggregate Maximum Bit Rate) as disclosed in Non-Patent Document 2 are set. Like the GBR handled by the GBR bearer, a PGW may discard packets in UE traffic exceeding APN-AMBR or UE-AMBR (which are generally called “AMBR”).
The PGW may discard a packet(s) when its flow rate exceeding the MBR or the AMBR. After the PGW discards a packet, a transmitting node uses the timeout of a retransmission timer as a trigger to detect that acknowledgement of the packet has not been received yet, or a mobile terminal (receiving side) uses the timeout of a packet receiving timer as a trigger to transmit a retransmission request which would cause retransmission and recovery of the discarded packet. However, since the actual discard of the packet has occurred before the detection of the timeout, the mobile terminal or an application consumes a wasteful latency to reduce communication efficiency significantly, causing a problem of reduction in convenience of the application.
Non-Patent Document 1 cited below discloses a method of using an ICMP (Internet Control Message Protocol) unreachable message (ICMP unreachable message) to adjust TCP (Transmission Control Protocol) retransmission timer on a transmitting node. This method can be applied to solve the above problem. In other words, a packet discard is notified to the transmitting node using the ICMP unreachable message to perform retransmission request processing so that the discarded packet can be retransmitted quickly without waiting the timeout of the packet retransmission timer.